Process for recovering the metal content of middlings, slags, low-grade ores, and concentrates



United States Patent PROCESS FOR RECOVERING THE METAL CON- TENT OF MIDDLLNGS, SLAGS, LOW-GRADE ORES, AND CONCENTRATES Nandor Wieder, Miskolc, Hungary, assiguor to Chemolimpex Magyar Vegyiaru Kulkereskedelmi Vallalat, Budapest, Hungary N0 Drawing. Filed Dec. 27, 1963, Ser. No. 333,997

4 Claims. (Cl. 75-108) This invention relates to a process for recovering the metal content of middlings, slags, low-grade ores and concentrates containing copper, cobalt, nickel, zinc, iron, manganese, or a mixture thereof, in a cyclic process, without evaporation.

It is known that the pyrometallurgical processing of low-grade oxide, hydroxide, carbonate, silicate or sulfide ores is not economical. These ores are, however, available in large quantities and, due to the exhaustion of the more opulent ore beds or to the lack of such beds, the economical processing of the low-grade ores is a very important but hitherto unsolved problem.

The physical dressing processes often give no satisfactory results; consequently, the employment of hydrometallurgical dressing methods would be needed to ensure that considerably less barren material gets to the pyrometallurgical processing and thereby the production of the metal be economical. However, the hydrometallurgical processes known hitherto are not suitable for processing ores in large quantities and are not economical.

The known hydrometallurgical processes are based on various principles. One of these methods employs the evaporation of the sulfate solution obtained by digesting the ore containing the metal to be recovered, and heating the obtained sol-id salt to a temperature exceeding the decomposition temperature of the metal sulfate. This process requires vast quantities of heat energy.

According to another method, the useful metal compound is precipitated from the sulfate solution with the aid of ammonia, or ammonium or sodium carbonates. In the case of this process, however, the total amount of the sulfuric acid used for leaching the ore and, in the case of using ammonium or sodium carbonates, also the carbonate salt, are lost.

It is known that the metal can be precipitated in the form of sulfides from the solution with the aid of hydrogen sulfide or alkali sulfides as well, but in the case of the hitherto-known processes this method can be economically employed only for precipitating small quantities of metal, because the production of the hydrogen sulfide and alkali sulfides is expensive and complicated.

The so-called Sweet process is used for processing lowgrade ores. In the case of this method the ore is roasted in the presence of solid ammonium sulfate at a temperature at which the ore is decomposed with the production of sulfur trioxide and ammonia. The metal content of the ore is digested by the sulfur trioxide, while the am monia is used for precipitating the metal leached by the aqueous solution. From the obtained ammonium-sul fate solution, the ammonium sulfate is regenerated with the aid of an expensive evaporation.

On the basis of the aforesaid it can be stated that the known hydrometallurgical processes serving for recovering the metal content of ores either need evaporation, or result in the total loss of the agents used for digestion, or for digestion and precipitation.

With the aid of the process according to the invention the disadvantages of the known hydrometallurigcal processes can be eliminated, and the metal content of lowgrade ores, middlings, slags and concentrates can be economically recovered in a cyclic process, without evaporation.

In the process according to the invention, the metal content of sulfide middlings, low-grade ores and concentrates containing a member selected from the group consisting of copper, cobalt, nickel, zinc, iron, manganese and mixtures thereof is recovered. According to this process the sulfide ores, middlings and slags are ground, the metal content to be recovered of the ground ores, middlings and concentrates is transformed to an aqueous metal-sulfate solution by sulfate roasting the ground ores, middlings and concentrates with gases containing oxygen, and by dissolving the obtained sulfated material with a solution containing -a member selected from the group consisting of alkali metal sulfates and ammonium sulfate in an "amount at least about stoichiometrically equivalent to the amount of the metal to be recovered, whereafter the obtained sulfate solution is separated from the insoluble residue, the metals to be recovered are precipitated from the sulfate solution in the form of metal sulfides with the aid of an aqueous solution of a polysulfide having a mol-arity about that of the alkali metal sulfates and ammonium sulfate contained in the sulfate solution, the amount of the polysulfides contained in the said aqueous polysulfide solution being about stoichiometrically equivalent to the amount of the metals to be precipitated in the form of metal sulfides, the obtained metal-sulfide precipitate is filtered, a past of the filtered sulfate solution containing alkali metalsulfates and/or ammonium sulfate is recovered with alkaline earth sulfides to an aqueous solution containing polysulfides, the said part of the said filtered solution having a volume about that of the polysulfide solution used previously for precipitating the metal sulfides, and the remaining part of the said filtered solution containing alkali metal sulfates and/or ammonium sulfate is used for transforming the metal content to be recovered of further ore quantities to an aqueous metal sulfate solution, and the precipitated metal sulfides are roasted to metal oxides.

In the process according to the invention, the metal content of middlings, slags, low-grade ores, and concentrates containing copper, cobalt, nickel, zinc, iron, manganese and a mixture thereof may be recovered by transforming the metal content to be recovered of the ground ores, middlings, slags, and concentrates to an aqueous sulfate solution by sulfate roasting the ground ores, middlings, slags and concentrates in the presence of gases containing sulfur dioxide. These gases may be preferably obtained by roasting metal-sulfide precipitates obtained previously in the cyclic process according to the invention by precipitating the metals to be [recovered with an aqueous solution of a p-olysulfide. The obtained sulfated material is dissolved with a solution containing alkali metal sulfates and/or ammonium sulfate in an amount at least about stoichiometrica-lly equivalent to the amount of the metals to be recovered, whereafter the obtained sulfate solution is processed in the same Way as described above in connection with sulfide middlings, low-grade ores and concentrates.

The metal content of middlings, slags, low-grade ores, and concentrates may be recovered also by transforming the metal content to be recovered of the ground middlings, slags, low-grade ores, and concentrates to an aqueous metal-sulfate solution, by dissolving the metal content to be recovered with the aid of sulfuric acid, in the presence of a solution containing alkali metal sulfates and/ or ammonium sulfate in an amount at least about stoichiometrically equavalent to the amount of the metals to be recovered, whereafter the obtained sulfate solution is processed in the same Way as described above.

Another method for recovering the metal content of middlings, slags, low-grade ores, and concentrates containing sulfides With the process according to the invention consists in transforming the metal content to be reco ered of the ground ores, middlings, slags, and concentrates to an aqueous metal-sulfate solution by leaching the ores, middlings, slags, and concentrates under pressures up to 200 at., at temperatures ranging from 100 to 250 C., in the presence of gases containing oxygen, with a solution containing alkali metal sulfates and/or ammonium sulfate in an amount at least about stoichiometrically equivalent to that of the metals to be recovered, whereafter the obtained sulfate solution is processed in the same way as described above.

The process according to the invention is further illustrated by the aid of the following examples.

Example 1 1000 kg. of an ore containing 18% of manganese, 10.5% of iron and 24% of SiO are ground and then pelletized. The pelletized substance is contacted in a sulfatizing roasting furnace with waste gases containing from 7 to 12% of S whereby the manganese is digested to mangenous sulfate. The material leaving the furnace is cooled and transferred into a dissolving container, in which the roasted ore is leached for 1-2 hours with 2900 l. of a solution containing 132 g./l. ammonium sulfate. Thereafter the solution is separated from the undissolved barren material. The obtained solution containing 55 g. of manganese in the form of sulfate and 132 g. of ammonium sulfate is fed into a vessel provided with a stirrer, inlet and outlet openings and corrosion-resisting lining, where the manganese is precipitated in the form of manganous sulfide with the aid of 2900 l. of a solution containing 41.5 g./l. of total sulfur, from which 32 g./l. sulfur is present in the form of sulfide. As a result of the process, 280 g. of manganous sulfide and 5800 l. of a solution containing 132 g./l. of ammonium sulfate are obtained.

The precipitation reaction of the manganous sulfide takes place very rapidly. Consequently, the slurry containing the manganous sulfate may be filtered after stirring for several minutes. The filtration may be advantageously carried out in a press or vacuum filter.

2900 l. of the pure ammonium-sulfate solution obtained as filtrate are used, after making up the loss of 4.6 kg. of ammonium sulfate, for leaching a further 1000 kg. of the ore. The other half of the filtrate is used, after making up the loss of 4.6 kg. of ammonium sulfate, for regenerating the ammonium polysulfide employed for precipitating the manganous sulfate, in a corrosion-resisting closed vessel provided with a stirrer, by reacting the solution at room temperature with a crude calcium-sulfide powder containing 290 kg. of active calcium sulfide, while stirring for 2-3 hours. In this way, the solution remains practically free of calcium, and its total sulfur content will attain 41.5 g./l., with a sulfide-sulfur content of 32 g./l. After this process, the solution to be used for precipitating the manganous sulfide is separated from the solid calcium sulfate in a filter press, and the calcium sulfate is again transformed to calcium sulfide. The pure ammonium-polysulfide solution passes from the filter press in a cyclic process into the vessel used for precipitating the manganous sulfide.

The manganous-sulfide precipitate is oxidizingly roasted with air in fluidizing roasting equipment. With the aid of the thus-obtained roasting gases containing from 7 to 12% of S0 or with the sulfuric acid prepared with the aid of this gas, the manganese content of further ore quantities is sulfatized.

From the roasted ore consisting of manganese oxides, the desired product containing manganese metal is produced by any of the known methods.

The same process may be used for processing ores containing, instead of manganese, copper, zinc, nickel or cobalt in similar or even in lower quantities.

Example 2 1000 kg. of a concentrate containing 10.8% of copper, 16.0% of zinc, 25.6% of iron, 39.0% of sulfur and 12.6% of insoluble materials are roasted in a fluidizing reactor at a temperature exceeding the temperature of decomposition of the iron sulfates, that is at about 700 C., the roasting being carried out sulfatingly for the copper and zinc. The roasted ore is leached with 5000 l. of a solution obtained as the filtrate of a previous precipitation and containing 135 g./l. ammonium sulfate and with 400 l. of washing water. The solution leaving the leaching equipment is sedimented and filtered. The 5000 l. of the solution obtained as filtrate contains 21.0 g./l. of copper (with a Cu-yield of 97.5%) and 30.0 g./l. of zinc (with a zinc yield of 93.7%). (The equivalent amount of the ammonium sulfate is 43.44-60.8=104.2 g./l.). From this solution the copper is precipitated with the aid of 1608 l. of a solution containing 69.5 g./l. of ammonium polysulfide. The obtained copper-sulfide precipitate is filtered, washed and oxidizingly roasted.

From the filtrate the zinc is precipitated with the aid of 2250 l. of a solution containing 69.5 g./l. ammoniumpolysulfide. The zinc-sulfide precipitate is filtered, washed and oxidizingly roasted.

From the ammonium-sulfate solution obtained as filtrate, after making up the loss in ammonium sulfate, 3858 liters are reacted with 450 kg. of crude calcium sulfide containing 70% of CaS and in this way, with a yield of a solution containing 69.5 g./l. ammonium polysulfide is obtained which is used for precipitating further metal sulfides. The remaining part of the filtrate is used for leaching further ore quantities. Instead of the calcium sulfide, barium or strontium sulfides may be used with equally good results.

The same method may be used if pure concentrates consisting of copper sulfide and zinc sulfide, or concentrates containing copper sulfide or zinc sulfide in a smaller amount, or concentrates containing copper sulfide and ferrous sulfide, or zinc sulfide and ferrous sulfide have to be processed.

Example 3 1000 kg. of a sulfide low-grade ore containing 0.8% of copper, 1.0% of zinc, 56.0% of iron (80.0% of 'Fe O and 18.2% of residue (from this 34% of sulfur) are sulfate roasted in a fluid reactor, and thus, with the aid of the sulfur content of the ore, by circulating the gases containing sulfur dioxide, the copper and zinc contents of the ore are transformed to sulfates. The roasted ore is leached with 4000 l. of a solution obtained previously as filtrate in the cyclic process and containing 82.5 g./l. of ammonium sulfate and with 600 l. of wash water, whereafter the slurry is sedimented and filtered. The filtrate contains 1.8 g./l. of copper and 2.2 g./l. of zinc.

The copper and zinc contents of the solution are precipitated with the aid of 400 l. of a solution containing 42.5 g./l. of ammonium polysulfide. After filtering and washing, the obtained sulfide precipitate is processed for copper and zinc in the same way as described in Example 2.

The solid material obtained after leaching the roasted ore contains no copper and zinc any more; consequently, it may be used for recovering its iron content.

The ammonium-sulfate solution obtained after filtering the sulfide precipitate is used in the way described in Example 2.

Example 4 1000 kg. of a low-grade ore containing 48.0% of iron (68.5% of Fe O 1 2.5% of lead and 19.0% of other substances are sulfate roasted in a furnace With gases containing sulfur dioxide, whereafter the roasted ore is leached with 400 l. of wash water. The obtained solution containing 51 g./l. ferrous iron (with an Feyield of 88%) is separated from the undissolved material, and is reacted with 8250 l. of a solution containing 62.0 g./l. of ammonium polysulfide. The obtained 695 kg. of ferrous sulfide are separated from the 16,500 1. of

mother liquor, and after washing are oxidizingly roasted.

The iron content of ores containing Fe O in lower or higher amounts, e.g. that of bauxites or slags may be recovered in a similar way.

The ammonium-sulfate solution obtained after filtering the sulfide precipitate is used in the way described in Example 2.

Example 5 1000 kg. of a low-grade ore containing 2.8% of copper in a form readily soluble in dilute sulfuric acid are leached with 4000 l. of a solution containing 20 g./l. of free sulfuric acid and 66.0% g./l. of ammonium sulfate and with 400 .1. of Wash water. After sedimentation and filtering, 4000 l. of a solution containing 6.4 g./l. of copper (with a Cu-yield of 91.6%) are obtained. The copper-content of this solution is precipitated by adding 800 l. of a solution containing 34.0 g./l. of ammonium polysulfide. After filtering and washing, the copper-sulfide precipitate is oxidizingly roasted to copper oxide. The same method may be used for treating low-grade ores containing, instead of copper, cobalt or nickel.

Example 6 1000 kg. of a concentrate containing 5.5% of nickel, 3. 8% of copper, 40.0% of iron, 35.0% of sulfur and 15.7% of silicium dioxide are leached in an autoclave at a temperature of 210 C., under an oxygen pressure of 35 at., with 4000 -l. of a solution containing 126- g./l. sodium sulfate and with 800 l. of wash water. The solution obtained after sedimentation and filtering contains 12.5 g./l. of nickel (with a Ni-yield of 91%) and 9.1 g./l. of copper (with a Cu-yield of 96%). From this solution the copper is first precipitated with 638 l. of a solution containing 69.5 g./l. of sodium sulfide. From the filtrate obtained after filtering the copper sulfide, the nickel is precipitated by adding 955 -l. of a solution containing 69.5 g./l. sodium sulfide. From the 5593 1. of the filtrate obtained after filtering the nickel sulfide, 1593 l. are used for regenerating the sodium-sulfide solution, and 4000 l. are used for leaching a further 1000 kg. of ore.

The 1593 11. of the filtrate are used for regenerating the sodium-sulfide solution by reacting the solution, after making up the loss in sodium sulfate, with 332 kg. of crude barium sulfide containing 80% of BaS, and in this way, with a yield of 90%, 1593 l. of a solution containing 69.5 g./l. sodium sulfide are obtained.

From the copper and nickel sulfides, the corresponding oxides are obtained by oxidizing roasting.

Concentrates and mattes of higher copper and nickel contents, as Well as also with cobalt content may be processed in similar way.

What I claim is:

1. A process for recovering the metal content of material consisting of sulfide middlings, low-grade ores and concentrates containing a metal selected from the class consisting of copper, cobalt, nickel, zinc, iron, manganese and mixtures thereof, comprising 1) grinding a said material,

(2) sulfate roasting the ground material with gases containing oxygen,

(3) dissolving the sulfated material in an aqueous solution of a member selected from the class consisting of alkali metal sulfates and ammonium sulfate in an amount at least about stoichiometrically equivalent to the amount of metal to be recovered,

(4) separating said solution from insoluble residue,

('5) adding to said solution an aqueous solution of a polysulfide selected from the class consisting of alkali metal polysulfide and ammonium polysulfide having a molarity about that of the alkali metal sulfate and ammonium sulfate in said sulfate solution, in an amount sufficient to precipitate the metal to be recovered in the form of metal sulfides,

(6) removing the metalsulfide precipitate from the solution,

(7) dividing the solution in two portions one of which is about equal in volume to said solution of step ('3) and the other of which is about equal in volume to said added solution of step (5),

(8) recycling said one portion from step (7) to step (9) reacting said other portion from step (7) With alkaline earth sulfide in an amount sufiicient to convert the sulfate of said other portion to the corresponding polysulfide, and

(10) recycling said other portion from step (9) to the liquids of the process passing through the steps of the process in a repeating cycle and substantially undiminished in volume.

2. A process for recovering the metal content of material consisting of middlings, slags, low-grade ores, and concentrates containing a metal selected from the class consisting of copper, cobalt, nickel, zinc, iron, manganese and mixtures thereof, comprising (1) grinding a said material,

(2) sulfate roasting the ground material 'with gases containing sulfur dioxide from step 1) hereinafter,

(3) dissolving the sulfated material in an aqueous solution of a member selected from the class consisting of alkali metal sulfates and ammonium sulfate in an amount at least about stoichiometrically equivalent to the amount of metal to be recovered.

(4) separating said solution from insoluble residue,

(5) adding to said solution an aqueous solution of a polysulfide selected from the class consisting of alkali metal polysulfide and ammonium polysulfide having a molarity about that of the alkali metal sulfate and ammonium sulfate in said sulfate solution, in an amount sutficient to precipitate the metal to be removed in the form of metal sulfides,

(6) removing the metal sulfide precipitate from the solution,

(7) dividing the solution in two portions one of which is about equal in volume to said solution of step (3) and the other of which is about equal in volume to said added solution of step (5),

(8) recycling said one portion from step (7) to (9) reacting said other portion from step (7) with alkaline earth sulfide in an amount sufficient to concert the sulfate of said other portion to the corresponding polysulfide.

(10) recycling said other portion from step (9) to step (5), and

(11) roasting the metal sulfide from step (6) to produce metal oxide and the gases of step (2),

the liquids of the process passing through the steps of the process in a repeating cycle and substantially undiminished in volume.

3. A process for recovering the metal content of material consisting of middlings, slags, low-grade ores and concentrates containing a metal selected from the class consisting of copper, cobalt, nickel, zinc, iron, manganese and mixtures thereof, comprising (1) grinding a said material,

(2) contacting the ground material with sulfuric acid in the presence of an aqueous solution of a member selected from the class consisting of alkali metal sulfates and ammonium sulfate with said member present in an amount at least about stoichiometrically equivalent to the amount of metal to be recovered, thereby to sulfate the material and bring the sulfated metal content thereof into solution,

(3) separating said solution from insoluble residue,

(4) adding to said solution an aqueous solution of a polysulfide selected from the class consisting of alkali metal polysulfide and ammonium polysulfide having a molarity about that of the alkali metal sulfate and ammonium sulfate in said sulfate solution, "in an amount sufiicient to precipitate the metal to be re covered in the form of metal sulfides,

( removing the metal sulfide precipitate from the solution,

(6) dividing the solution in two portions one of which is about equal in volume to said solution of step (2) and the other of which is about equal in volume to said added solution of step (4),

(7) recycling said one portion from step (6) to step (8) reacting said other portion from step (6) with alkaline earth sulfide in an amount sufiicient to convert the sulfate of said other portion to the corresponding polysulfide, and

(9) recycling said other portion from step (8) to step the liquids of the process passing through the steps of the process in a repeating cycle and substantially undiminished in volume.

4. A process for recovering the metal content of material consisting of middlings, slags, low-grade ores and concentrates containing sulfides and a metal selected from the class consisting of copper, cobalt, nickel, zinc, iron, manganese and mixtures thereof, comprising (1) grinding a said material,

(2) leaching the ground material under superatmospheric pressure at a temperature between about 100 C. to about 250 C. in oxidizing contact with gases containing oxygen in an aqueous solution of a member selected from the class consisting of alkali metal sulfates and ammonium sulfate in an amount at least about stoichiometrically equivalent to the amount of metal to be recovered, thereby to convert the metal content to metal sulfate,

(3) separating said solution from insoluble residue,

(4) adding to said solution an aqueous solution of a polysulfide selected from the class consisting of alkali metal polysulfide and ammonium polysulfides having a molarity about that of the alkali metal sulfate and ammonium sulfate in said sulfate solution, in an amount sufficient to precipitate the metal to be recovered in the form of metal sulfides,

(5) removing the metal sulfide precipitate from the solution,

(6) dividing the solution in two portions one of which is about equal in volume to said solution of step (2) and the other of which is about equal in volume to said added solution of step (4),

(7) recycling said one portion from step (6) to (8) reacting said other portion from step (6) with alkaline earth sulfide in an amount sufficient to convert the sulfate of said other portion to the corresponding polysulfide, and

(9) recycling asid other portion from step (8) to the liquids of the process passing through the steps of the process in a repeating cycle and substantially undiminished in volume.

References Cited OTHER REFERENCES Adsorption on Inorganic Materials, ORNL-3488, UC-4 Chemistry, TID-4500 (22nd ed.). Received in Scientific Library of the US. Patent Office on Oct. 31,

Phillips et al., Adsorption on Inorganic Materials, V. Reaction of Cadmium Sulfide with Copper (11), Mercury (II), and Silver (1), Journal of the American Chemical Society, vol. 85, Feb. 20, 1963, pp. 486-487.

HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

N. F. MARKVA, Assistant Eafiaminer. 

1. A PROCESS FOR RECOVERING THE METAL CONTENT OF MATERIAL CONSISTING OF SULFIDE MIDDLINGS, LOW-GRADE ORES AND CONCENTRATES CONTAINING A METAL SELECTED FROM THE CLASS CONSISTING OF COPPER, COBALT, NICKEL, ZINC, IRON, MANGANESE AND MIXTURES THEREOF, COMPRISING (1) GRINDING A SAID MATERIAL, (2) SULFATE ROASTING THE GROUND MATERIAL WITH GASES CONTAINING OXYGEN, (3) DISSOLVING THE SULFATED MATERIAL IN AN AQUEOUS SOLUTION OF A MEMBER SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL SULFATES AND AMMONIUM SULFATE IN AN AMOUNT AT LEAST ABOUT STOICHIOMETRICALLY EQUIVALENT TO THE AMOUNT OF METAL TO BE RECOVERED, (4) SEPARATING SAID SOLUTION FROM INSOLUBLE RESIDUE, (5) ADDING TO SAID SOLUTION AN AQEUOUS SOLUTION OF A POLYSULFIDE SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL POLYSULFIDE AND AMMONIUM POLYSULFIDE HAVING A MOLARITY ABOUT THAT OF THE ALKALI METAL SULFATE, IN AN AMOUNT SUFFICIENT TO PRECIPITATE THE METAL TO BE RECOVERED IN THE FORM OF METAL SULFIDES, (6) REMOVING THE METAL SULFIDE PRECIPITATE FROM THE SOLUTION, (7) DIVIDING THE SOLUTION IN TWO PORTIONS ONE OF WHICH IS ABOUT EQUAL IN VOLUME TO SAID SOLUTION OF STEP (3) AND THE OTHER OF WHICH IS ABOUT EQUAL IN VOLUME TO SAID ADDED SOLUTION OF STEP (5), (8) RECYCLING SAID ONE PORTION FROM STEP (7) TO STEP (3), (9) REACTING SAID OTHER PORTION FROM STEP (7) WITH ALKALIN EARTH SULFIDE IN AN AMOUNT SUFFICIENT TO CONVERT THE SULFATE OF SAID OTHER PORTION TO THE CORRESPONDING POLYSULFIDE, AND (10) RECYCLING SAID OTHER PORTION FROM STEP (9) TO STEP (5), THE LIQUIDS OF THE PROCESS PASSING THROUGH THE STEPS OF THE PROCESS IN A REPEATING CYCLE AND SUBSTANTIALLY UNDIMISHED IN VOLUME. 